Oxidation-stable grease composition



Patented Feb. 1,

omparroN- s'ranm amnesia COWGSETION No Drawing. Application February 6, 1942, Serial No. 429,768

7 Claims. ('01. 252-40) This invention relates to the stabilization of grease compositions and particularly those grease compositions which are oxidation-unstable by incorporating in said greases an oxidationstabilizer such as amino salicylic acid.

One of the problems encountered in the usual manufacture of greases is the susceptibility of the finished grease to oxidation during storage or when subjected to severe operating conditions such as heavy loads and high temperatures. This tendency toward oxidation results in partial decomposition of the grease which manifests itself in the appearance of a red to brownish colored hard surface film, and a separation of soap and oil, together with an increase in the free fatty acid content. In service the resulting oxidation reaction breaks down the grease structure and causes corrosion, pitting and even seizure of bearings or moving parts packed therewith.

/ According to the present invention, an oxidation-stable grease composition may be obtained by incorporating in a grease a. small proportion of an amino salicylic acid. The resulting grease composition retains its structure and homogeneity over extended periods of time even under severe oxidizing conditions, without any efiects on its lubricating qualities. The range of utility of this type of oxidation-stabilizer extends from the liquid greases'containing 0.5%. soap to the sponge and brick type greases containing up to approximately 40% soap and may be added to these compositions during one of the usual-manulecturing steps or incorporated in the finished product by means of additional processing. In the preferred procedure the stabilizer is added to the product in a concentrate of mineral oil just prior to the drawing of the grease.

The type of soap base, whether it be soda, lime, aluminum, lithium or mixed soap base is not critical as the. present inhibitor is adaptable to any type of grease which is susceptible to oxidation as measured by the increase in free fatty acid content. However, for the purpose of this invention, the preferred types of soap bases are a lime soap and mixed soda-lime soap base. These soap bases may be compounded with a mineral oil within the range of '70 Saybolt viscosity at 100 F.

to 200 Saybolt viscosity at 210 F. and includes such oils as distillates, residuals or cylinder stock oils. Here again the type of compounding oils does not form a limitation to the inhibitor and is only dependable upon the type of service for which the grease is intended.

The amount of the amino salicylic acid generally used to attain oxidation stability depends 'five or more carbon atoms.

upon the composition of the particular grease and its normal degree of oxidation susceptibility. The range of proportions which would normally cover its use in the more common types of greases is within the range of from 0.05 to 2.5% by weight of the finished grease composition. In the majority of cases, optimum results may be obtained by the use of 0.1 to 1.5% by weight of the stabilizer.

The amino salicylic acids may be defined as those derivatives of salicylic acid which contain one or more amino groups attached to the arcmatic nucleus. If necessary, oil solubility may be increased by introducing into the aromatic nucleus a solubilizing radical such as a high molecular weight aliphatic substituent containing For the purposes of the present invention, 5-amino salicylic acid will be used to illustrate the effectiveness of thisclass of compounds in providing oxidation stability to grease compositions.

These stabilizers are usually dissolved or dispersed in a mineral oil to obtain a concentrate which facilitates the incorporation of the stabilizer in the grease. The mineral oil of the concentrate is preferably the sameas the mineral oil contained in the grease composition to be stabilized. If the stabilizer is to be added during the course of manufacture, the concentrate is blended with the compounding oil and added during the last stage of processing, along with the residual compounding oil. The amount of concentrate added is based on the desiredstabilizer content of the finished grease. Another method of incorporating the stabilizer is by processing the concentrate into the finished grease. This is done by heating the grease in a kettle while stirring until the mass is fluid and then adding the desired amount of concentrate. The mixture is thereafter stirred to a homogeneous mass and then drawn.

For purposes of illustration, a mixed soda-lime soap grease, used in the lubrication of ball and roller bearings, was inhibited with varying amounts of 5-amino salicylic acid and subjected to an oxidation stability test. The particular test used is commonly referred to as the "Accelerated Norma-Hoffman Stability Test? and is described in the proceedings of the AmericanSociety for Testing Materials, volume 38, part II, 1938, in an article entitled Some Applications of an Acceler- 110 pounds of oxygen at 210 F. for 100 hours or until the pressure has dropped 35 pounds.

Two representative samples of grease having the following calculated compositions were used as the reference greases:

Varying amounts of 5 -amino salicylic acid were added to the reference greases A and B and subjected to the foregoing test conditions. The results of the test are as follows:

I 1 Pressure I Hours Average. frvv drop I run fatty acid I Pounds Per can! Grease A .1, 35 29 3.3 Grease A+0.1'j;' i I cid 36 79 Li 8.... i 5' 1001 0..- GI'LBSPB....... A :15 40! 3.1 Grease B+0 5"}, S-aminu salicylic mirL. J 100 L1 (vrcasc B -mninu salicylic acid H 100 1.4

The exceptional results shown .by the foregoing oxidation test exemplifies the excellent oxidation stabilizing effect of the amino salicylic acids. This effect is not limited to a soda-lime soap grease but applies as well to any metallic soap grease which is susceptible to oxidation as measured by the free fatty acid content.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A grease composition comprising a homogeneous mixture or a mineral oil, soap and a small proportion of an amino salicylic acid.

2. A grease composition comprising a homogeneous mixture of a mineral oil, metallic soap and 0.05-2.5% by weight of an amino salicylic acid.

3. A method of rendering a grease composition oxidation-stable, which comprises intimately incorporating with said grease composition a relatively small proportion of an amino salicylic acid.

4. A grease composition comprising a homogeneous mixture of a mineral oil, a soda-lime soap, and (Ll-1.5% by weight of 5-amino salicylic acid.

5. A grease composition comprising a homogeneous mixture of a mineral lubricating oil, a soda soap, and 0.11.5% by weight of 5-amino salicylic acid.

6. A grease composition comprising a homogeneous mixture of a mineral lubricating oil, a lime soap, and 0.11.5% by weight of S-amino salicylic acid.

7. A grease composition comprising a homogeneous mixture of a mineral lubricating oil, a metal soap and a small amount of an amino salicylic acid suiiicient to render said mixture oxidation-stable.

LYNN R. S'I'RAWN. 

